There has been known an electrodialyzer which carries out desalination and concentration, utilizing a DC current as a driving power source.
Such an electrodialyzer has many anion exchange membranes and many cation exchange membranes disposed alternately with a chamber frame interposed between adjacent anion and cation membranes and has electrodes disposed on both ends so as to form desalination chambers and concentration chambers between the membranes. The chamber frames may be capable of having a desired service temperature by being produced from a material properly chosen among a various kinds of olefin-based thermoplastic resins.
Each of the chamber frames has been produced as described below. First, a sheet made of an olefin-based thermoplastic resin is cut in a picture frame having an opening in a central part thereof, forming a frame portion of a chamber frame. At the time of forming the frame portion, a liquid supply port and a liquid discharge port are also formed in the frame portion such that a liquid to be treated can pass therethrough.
Then, in order to secure a liquid flow path toward the central opening of the chamber frame from the liquid supply port and the liquid discharge port, distributors are fitted into the chamber frame by injection welding. Next, a polyolefin net, which serves as a spacer for the chamber frame with the distributors fitted thereinto, is positioned so as to cover the central opening of the chamber frame. Then, the net is temporarily welded to the frame portion at plural locations by an ultrasonic spot welder.
After that, this semi-finished product with the net temporarily welded thereto is finished as a finished product by using the ultrasonic spot welder to integrally weld the frame portion and the net with the welding process being divided into several steps.
This method, however, has suffered from breakage of an ion exchange membrane, an adverse effect upon dialysis performance due to an increase in the amount of liquid leak during use of a chamber frame produced by this method, and another problem, which are caused by sag of the net caused during temporarily welding, the occurrence of a wrinkle caused by division of a welding process into several steps, the presence of a large thickness irregularity in the welded portions of the olefin-based thermoplastic resin and the polyolefin net.
Further, various studies from several aspects have been made with regard to the simplification in the working process. For example, there has been proposed a method for using a chamber frame made of a foamed member having a lower deformation temperature to heat than a net as a spacer such that the chamber frame and the net can be integrated by heat (see Patent Document 1 listed below).